1. Field of the Invention
This invention relates to a bearing and a medical X-ray diagnostic apparatus using the same. More particularly, the invention relates to an X-ray diagnostic apparatus having a support mechanism rotatably structured with supporting a C-formed arm oppositely provided with an X-ray tube and an imager.
2. Description of the Related Art
In the X-ray diagnosis concerning the region including the circulatory system, particularly the heart, it is conventionally desired to conduct a stereoscopic observation by taking X-ray images in a multiplicity of directions. For this reason, there is an X-ray diagnostic apparatus having a C-formed arm (hereinafter, referred to as a C-arm) having, at one end, an X-ray tube and, at the other end, an imager including an image intensifier (I. I.) and a television camera unit (TV camera) wherein the C-arm is allowed to rotate or slide in a C-form direction.
The X-ray diagnostic apparatuses, having such C-arms, includes, say, a fix-type X-ray diagnostic apparatus (JP-A-2001-137222). FIG. 1 is a perspective view showing a fix-type X-ray diagnostic apparatus. As shown in FIG. 1, the fix-type X-ray diagnostic apparatus is constructed with a stand 45, a column 44 rotatably supported on the stand 45 about a column's rotary axis vertical to the floor, a C-arm 42 having an X-ray tube 40 and an imager 41, and an arm support 43 rotatably supported on the column 44 about a main rotary axis orthogonal to the column's rotary axis and holding the C-arm 42 slidable along the C-form. In this case, the support mechanism structured for horizontal rotation refers to the column 44.
FIG. 2 shows a sectional view of the rotary mechanism supporting the column 44 horizontally rotatably. As shown in FIG. 2, the column 44 is supported on the stand 45 through a bearing 50.
However, the bearing 50 cannot support the column in a manner not to rotate due to the inertia force caused upon sliding the C-arm 42 or upon rotating it about the main rotary axis.
Accordingly, there is a need to provide a rotary support mechanism in order to prevent the column from rotating due to the inertia force caused by movement of the C-arm. For example, it is a practice to employ an electromagnetic brake having an electromagnet 51 on the column 44 side so that the column 44 can be fixed on the stand 45 by energizing the electromagnet 51 and attract the electromagnet 51 to the attractive member 52 on the stand 45 side. Besides such an electromagnetic brake mechanism, there are cases to employ a structure having a self-lock mechanism in the speed reducer.
Namely, the mechanism is complicated because of the necessity of a rotary support mechanism for supporting the column not to rotate in addition to the rotary mechanism supporting the column 44 for horizontal rotation. Meanwhile, in order to secure the torque for holding the column not to rotate, there is a need to use a large-sized electromagnet or attaching an electromagnet in a position greatly distant from the column's rotary axis. Accordingly, the periphery of the rotary mechanism is inevitably size-increased because of providing a rotary support mechanism for supporting the column not to rotate. Meanwhile, it also constitute a factor to size-increase the apparatus overall besides the periphery of the rotary mechanism.